Today ScottGu announced on his blog the release of a public beta of the upcoming .NET 3.5 SP1 and VS 2008 SP1 releases planned for "this summer as free updates"
There are a few important installation notes, and a reminder that this is a beta, but there are also a bunch of very cool improvements. Scott's blog post goes into many of the details for web developers and VS2008 in general and Tim has a post going into specifics relating to WPF.
Download links of goodness: